A technology for measuring a three-dimensional shape of a subject on the basis of a captured image. Such a technology is employed in various technical fields. One example is a biometric authentication device such as a palm vein authentication device.
In the palm vein authentication device, when imaging biological data to be registered, a position of a hand, which is an example of the subject, is guided by a well-known guiding member or the like. However, there are cases in which a guiding member that guides the position of the hand when performing collation is not provided. When biological data of a hand that is not guided by a guiding member is imaged, a great difference may be generated between registration data and collation data due to a difference in the position of the hand, a tilt of the hand, or the like, and a success rate of personal authentication may be reduced.
One example of a method for solving the problem above is a method for measuring a posture such as a tilt of a hand and making correction to cancel deviation in the posture of the hand when performing collation. In this method, the posture of the hand can be detected by using a plurality of distance sensors so as to measure a distance from the respective distance sensors to a corresponding portion of the hand. However, in order to improve an accuracy in measuring the posture of the hand, a large number of distance sensors need to be used. Therefore, a cost for a biometric authentication device increases, and a size of the biometric authentication device also increases. Further, when the biometric authentication device has physical restrictions on a size or the like, it is very difficult to arrange the large number of distance sensors within the restrictions while maintaining a prescribed accuracy or more in measuring the posture of the hand.
Meanwhile, the Shape From Shading (SFS) technique for measuring a three-dimensional shape of a subject on the basis of an luminance value distribution of an image of a subject that is captured while the subject is being irradiated with illumination light is known (see, for example, Non-Patent Documents 1-3). By employing the SFS technique to measure a posture of a hand, distances from a light source to a large number of points can be measured without using a large number of distance sensors, and the posture of the hand can be detected with a higher accuracy.    [Patent Document 1] Japanese Laid-open Patent Publication No. 2007-10346    [Non-Patent Document 1] R. Kimmel et al., “Global Shape from Shading”, CVGIP: Image Understanding, pp. 120-125, 1994    [Non-Patent Document 2] R. Zhang et al., “Shape from Shading: A Survey”, IEEE PAMI (Transactions on Pattern Analysis and Machine Intelligence), Vol. 21, No. 8, pp. 690-706, August 1999    [Non-Patent Document 3] E. Prados et al., “Shape from Shading: a well-posed problem?”, INRIA, No. 5297, pp. 1-55, August 2004